Low loop height ball bonding method and apparatus

ABSTRACT

In accordance with the invention, a bump is formed on top of a die bond pad by forming a ball bond there. Then, without severing the wire, the capillary undergoes a set of coordinated motions to fold the wire on top of the ball bond. The wire is then bonded on top of the ball bond bump without severing the wire. This is then followed by a further set of coordinated xy motions to from the loop and bring the capillary over the second bond site (e.g., on the lead frame). The wire is then stitch bonded to the second bond site and the tail severed to complete the wire loop interconnect.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 10/988,053 filed Nov. 12, 2004, which claims priority to U.S.Provisional Patent Application No. 60/525,305 filed Nov. 26, 2003 thecontent of which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention pertains to wire bonding on semiconductor devices.

BACKGROUND OF THE INVENTION

Ball bonding is a common technique for interconnecting the bond pads ona semiconductor die with the contact points on a lead frame or othersubstrate on which the die is mounted. Electrical interconnect wirestypically are run from the bond pads on the top of the die to leadfingers on a lead frame in order to electrically connect the circuitryon the die to the pins of the lead frame that will extend from thepackage after the die has been encapsulated. The wire bonds between thebond pads of the die and the lead fingers commonly are formed using aball bonding machine. FIGS. 1A-1I demonstrate the steps in aconventional technique of ball bonding. The conventional loopingtechnique (herein termed forward looping) involves ball bonding one endof a gold wire to a bond pad on a die and stitch bonding the other endof the wire to the lead frame. More particularly, using a ball bondingmachine, the wire 17 is passed through a set of clamps 18 and through acenter bore of a capillary 11. At the beginning of the process, a wire“tail” 23 is protruding from the tip of the capillary 11, as shown inFIG. 1A. The tail 23 at the end of the wire 17 is heated by means of anelectric spark 16 termed an electric flame off (EFO) from an EFO wand24. The spark melts the end of the wire, which, in turn, forms into aball 19 when melted, as shown in FIG. 1B. The clamps 18 are closedduring EFO in order to provide a current return path through the clampsand then are opened to allow the ball to seat itself in the capillarytip. The capillary 11 is then moved to a position above the bond pad 13of the die 15, as shown in FIG. 1C.

The capillary 11 is then moved downwardly with the clamps 18 still openduring the initial acceleration of the capillary and then are closedduring deceleration of the capillary so that the ball remains seatedduring the downward motion of the capillary. The clamps then open justbefore the ball contacts the bond pad 13. The ball 19 comes into contactwith the bond pad 13 on the die 15 with the clamps 18 still open, asshown in FIG. 1D. Heat and/or ultrasonic energy are applied to the dieto cause the ball to become bonded to the bond pad 13. This bondtypically is termed a ball bond or first bond. The capillary 11 is thenraised with the clamps 18 opened to pay out a short length of wire thatis still attached to the top of the ball bond, as shown in FIG. 1E.Next, with the clamps 18 open, the capillary 11 is moved through apredetermined looping motion with the wire (which is still connected tothe ball bond) and trailing out of the capillary 11 to a positiongenerally near and above the lead finger 21. With the capillary 11positioned above the lead finger 21, the clamps 18 are closed, as shownin FIG. 1F. The capillary 11 is then lowered to pinch the wire betweenthe capillary and the surface of the lead finger 21, as shown in FIG.1G. Again, heat and/or ultrasonic energy may be applied to bond thepinched portion of the wire to the lead finger 21. This bond is termed astitch bond or second bond. The clamps 18 are now opened again and thecapillary 11 is then raised with the wire still attached to the stitchbond such that an additional wire “tail” 23 pays out of the capillary,as illustrated in FIG. 1H. The clamps 18 are then closed and thecapillary 11 is raised further to snap the wire tail 23 at the weakestpoint, which is at the stitch bond location. The completed connection 22is termed a wire loop and is illustrated in FIG. 11.

At this point, the capillary is moved near the next bond pad on the die15 for commencing the wire looping process for the next bond pad on thedie. The wire tail 23 that remains protruding from the tip of thecapillary after the conclusion of the formation of the preceding wireloop will be melted by EFO, as previously described, to form the nextball for commencing the next ball bonding operation. The above-describedconventional forward ball bonding technique is fast, reliable, andinexpensive. However, it has limitations. Most notably, the minimal loopheight is normally over 150 microns. Loop height is defined as themaximum height of the wire above the bonding surface, e.g., the topsurface of the bond pad. Attempting to achieve lower loop height cancause neck damage to the wire loop. The neck is the portion of the wireloop directly adjacent to the ball bond. Reducing the loop height below150 microns tends to weaken or break the neck.

There is an increasing demand for smaller and smaller integrated circuitpackaging. One of the significant aspects of reducing the size of theintegrated chip packaging is reducing its thickness or height. Thethinner packages are generally referred to in the trade as low profilepackages. Commensurate with the desire to reduce the height of thepackage is the desire to reduce the height of the highest point of thewire loops, which, in many instances, is the limiting factor as to theheight of an integrated circuit package.

In order to reduce loop heights for integrated circuit packaging andother purposes, a wire looping technique known as reverse looping wasdeveloped. The premise behind reverse looping is that, because thehighest point of the wire loop is adjacent the ball bond, it would bedesirable reverse the looping process so as to make the first, ball bondon the lead frame (or other substrate) and make the second, stitch bondon the bond pad of the die because the surface of the lead frame islower than the surface of the die. Hence, the highest point of the wireloop is near the lower bonding surface, thus reducing the overallheight.

However, simply reversing the direction of the looping process would notbe possible because, the stitch bond requires the capillary to come incontact with the bonding surface. The bond pads on a die usually arevery small and, thus, it is difficult to make a stitch bond on a bondpad on a die without the capillary contacting and, hence, damagingsurrounding circuitry on the die. Furthermore, the wire loops tends tosag to their lowest points close to the stitch bond. Thus, if the stitchbond site is higher than the ball bond site, the wire might contact theedge or the top surface of the die. This could lead to electrical shortsor breakage of the wire.

Thus, a reverse looping technique was developed, such as illustrated inFIGS. 2A through 2C, in which the first step is to form a ball bond 25on top of the bond pad 27 on the die 29 essentially in accordance withstandard techniques for forming ball bonds. However, instead of payingout the wire 17 as would be the case after making the ball bond in aconventional forward looping technique, the capillary 11 is raised, theclamps 18 are closed, and the capillary is raised further to snap thewire off from the ball bond leaving just the ball bond (or bump) 25 onthe bond pad 27, as illustrated in FIG. 2A. Then a complete wire loopingprocess is performed in the reverse direction, i.e., from the substrateto the bond pad. That is, a second ball bond 37 is then formed on thelead frame 39, the capillary 11 is then moved through a series ofmotions to a position above the first ball bond 25 to create the desiredwire loop shape, as illustrated in FIG. 2B. Then, a bond 43 is formed ontop of the first ball bond (or bump) 25. The completed wire loop isillustrated in FIG. 2C.

This reverse looping process can provide low loop heights for lowprofile packaging. However, it is a much slower process than forwardlooping because it requires the formation of two ball bonds per loop.Furthermore, the die must suffer greater impact because the capillarymust form a bond on the die twice per wire loop (i.e., once to createthe first ball bond and a second time to create the bond on top of theball bond). Another limitation of reverse looping is that it often isthe limiting factor on how fine the pitch of the bond pads on the die.Particularly, the bump 25 on top of the die bond pad must be largeenough to provide support for a bond. In addition, the diameter of thebump will increase in the lateral direction when the bond is made on topof it.

Accordingly, it is an object of the present invention to provide animproved wire loop formation method and apparatus.

It is another object of the present invention to provide a wire loopinterconnect with very low loop height.

SUMMARY OF THE INVENTION

In accordance with the invention, a bump is formed on the die bond padby forming a ball bond thereon. Then, without severing the wire and withthe clamps open, the capillary undergoes a set of coordinated xyzmotions to fold the wire on top of the ball bond. Then the wire isbonded on top of the bump without breaking off the tail. This isfollowed by a further set of coordinated xyz motions to bring thecapillary to the second bond site (e.g., the lead frame or othersubstrate) and perform a, stitch bond on the substrate and then breakoff the tail to complete the process.

In accordance with one particular embodiment of the invention for makingthe aforementioned wire fold, the ball bond is made and then thecapillary is raised in the z direction a designated height (hereintermed the separation height). It is then moved horizontally (in the xyplane) a specified distance in a direction generally away from thesecond bond location (herein termed the fold offset distance). Thecapillary may or may not be raised again in the z direction by anotherdistance (herein termed the fold factor). This is followed by anothermotion in the xy plane to generally bring the capillary back to the topof the bump for formation of the aforementioned bond on top of the bump.This is then followed by another coordinated xyz motion to bring thecapillary to the location of the second bond site (e.g., on the leadframe) where the stitch bond will be made.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1I are elevation views illustrating the steps of aconventional forward looping operation.

FIGS. 2A through 2C are elevation views illustrating steps of a reverselooping operation.

FIG. 3 is a pictorial elevation view of a folded wire loop interconnectin accordance with the present invention.

FIG. 4 is a pictorial elevation view showing the various components ofthe set of xyz motions involved in forming a folded bump in accordancewith the present invention.

FIGS. 5A through 5O are elevation views illustrating the steps of afolded forward looping operation in accordance with the presentinvention.

FIG. 6 is a pictorial elevation view showing the various components ofthe set of xyz motions involved in forming a folded bump in accordancewith particularly preferred exemplary embodiment of the invention.

FIG. 7A is a side view of a bump and a fold of a wire formed on the bumpformed using the exemplary parameters set forth in FIG. 6; and FIG. 7Bis a stitch bond.

FIGS. 8A and 8B are scanning electron micrographs of a completed loopproduced after forming the bump shown in FIG. 7A.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3 is a side elevation pictorial of a folded forward wire loop 45formed in accordance with the present invention. FIG. 3 shows anintegrated circuit die 51 including a bond pad 53 on its top surface anda lead frame substrate 55 with a wire loop interconnect between the bondpad 53 and the lead frame 55. The wire loop 45 is formed in accordancewith the technique of the present invention may be considered tocomprise five general components. With reference to FIG. 3, they are (1)a bump 56, (2) a wire fold 57 on top of the bump, (3) a bond on top ofthe bump 58, (4) a wire loop 59 that interconnects the first and secondbond sites, and (5) a stitch bond 60 at the second bond site.

The five general components described above may be formed using a ballbonding machine.

FIGS. 5A through 5O illustrate the position of the capillary of the ballbonding machine and the condition of the wire at various stages of anexemplary process for forming a folded forward wire loop in accordancewith one particular embodiment of the present invention. In theterminology used in this specification, the vertical direction is termedthe z direction and the horizontal direction is termed the xy direction.The Figures in this application are, of course, two dimensional so thatall xy motions are illustrated as being in the plane of the page andthus could be considered simply as one dimensional movements, i.e., x ory, rather than xy. However, because, in the real world, the wire loopson a given die are not all parallel to each other, all lateral motionmust be defined as xy motions in the machine code that controls themotion of the capillary of a ball bonding machine. Thus, we use the sameterminology in this specification. In addition, the terms vertical andhorizontal are merely exemplary based on the assumption that the topsurface of the die is oriented horizontally, which is typical, but notnecessarily always an accurate assumption.

As shown in FIG. 5A, the folded forward loop formation process beginswith the capillary 11 at the end of the preceding looping process with awire tail 23 extending from the capillary and the clamps 18 closed. Thecapillary is positioned in the vicinity of the bond pad 61 of the die 63and the associated lead finger 65 between which the next wire loopinterconnect is to be made.

The wire is melted with the electric-flame-off 67 to cause the end of itto melt. Upon melting, it inherently forms into a ball 72, as shown inFIG. 5B. The capillary is lowered and moved toward the bond pad 61, asshown in FIG. 5C. The capillary is then lowered to contact the ball 72against the bond pad 61. Heat and/or ultrasonic energy is applied tobond the ball to the bond pad. FIG. 5D shows the process at this point,which essentially is the end of the formation of the first portion ofthe folded forward wire loop, i.e., the bump 56.

Next, the capillary 11 rises with the clamps 18 open in order to pay outa length of wire extending from the top of the bump 56. The distance ofthis rise is herein termed the separation height, and is illustrated at75 in FIG. 4. FIG. 5E shows the capillary position after this step. Thecapillary 11 then moves in the xy plane in a first direction generallyopposite the direction to the second bond site 65 (to the left in FIGS.5A through 5O). Preferably, the direction of the fold offset is exactlyopposite the xy direction toward the second bond site 65, however, itcan be in any direction. In fact, there may be cases in which it iszero. The distance of this xy motion is herein termed the fold offsetand is shown in FIG. 4 at 76. The position of the capillary after thefold offset motion is shown in FIG. 5F.

In some embodiments of the invention, at the end of the fold offsetmotion, the capillary 11 is raised again (in the positive z direction) ashort distance (herein termed the fold factor) to pay out additionalwire. The fold factor is shown at 77 in FIG. 4. However, in someapplications of the invention, a fold factor of zero will be adequate.FIG. 5G shows the position of the capillary and wire at this point inthe process. The fold offset and the fold factor control the amount ofwire in the wire fold.

The capillary 11 is then moved back toward the bump 56 to fold the wireback over on top of itself to begin forming the wire fold on top of thebump. FIG. 5H shows the position of the capillary 11 and the conditionof the wire as the capillary is moving to form the fold. Thislast-mentioned motion is herein termed the fold return motion as isillustrated at 78 in FIG. 4. Preferably, the fold return motion is inthe xy direction exactly opposite the xy direction of the fold offsetmotion. In those embodiments in which the fold factor 77 is zero, thefold return motion preferably is a purely horizontal (i.e., xy) motion.If the fold factor 77 was not zero, the fold return motion 78 mayinclude a negative z component to return the capillary to the sameheight that it was during the ball bonding. Either case returns thecapillary to the separation height at the end of the fold return motion.However, this is not a requirement. In fact, in at least some preferredembodiments of the invention, as discussed further below, the capillaryreturns to a height below the separation height In fact, the fold returnmotion 78 may include a positive (upward) or negative (downward) zcomponent, even if the fold factor 77 was zero. The important aspect isthat a wire fold is formed on top of the bump 56 preferably extending ina direction directly away from the second bond site 65. The differencebetween the separation height and the position of the capillary at theend of the fold return motion 78 is herein termed the bump height. Itmay be a positive or a negative number. However, as noted previously, insome implementations of the invention, there will be no z motion of thecapillary between reaching the separation height and completion of thewire fold and/or the fold factor and the z component of the fold returnmotion will be exactly equal and opposite so that the bump height willbe zero.

Furthermore, the horizontal component of the fold return motion 78 neednot be the same distance as the fold offset motion. Depending on theparticular application, it may be desirable to return to a position forpurposes of performing the bond at a position that is short of (asillustrated by path 78 a in FIG. 4), exactly the same as (as illustratedby path 78 b in FIG. 4), or long of (as illustrated by path 78 c in FIG.4) the original xy coordinates of the capillary prior to the fold offsetmotion.

In those rare embodiments in which the fold offset is zero, thehorizontal component of the fold return motion also may be zero or verysmall. However, it need not be since, as just noted, it may be desirablein certain circumstances that the bond on top of the bump be made shortof or long of the original xy coordinates of the capillary prior to thefold offset motion (i.e., the original xy coordinates of the capillarywhen it made the bump when it made the bump). Generally, however, thereshould be at least either a non-zero offset motion or a non-zerohorizontal component to the fold return motion in order to cause theloop to form in some specified direction. In the absence of both, thedirection of the fold that the wire takes may be unpredictable and/ormay vary from bond to bond. In the absence of any significant horizontalmotion in both the fold offset motion and the offset return motion,there may be no folded loop formed at all or a negligible one. This mayactually be desirable in some circumstances.

The horizontal difference between the xy coordinates of the capillary atthis point relative to the xy position of the capillary when the bumpwas formed is termed the fold return offset. In other words, the foldreturn offset is the difference in the xy dimension between the foldoffset motion and the horizontal component of the fold return motion. Ifthe xy component of the fold return motion 78 is less than the foldoffset motion 76, the fold return offset is represented as a positivenumber. If the horizontal component of the fold return motion 78 islonger than the fold offset motion 76, the fold return offset isrepresented as a negative number. If the fold offset motion 76 and thefold return motion 78 have the same xy (i.e., horizontal) magnitudes,then the fold return offset is zero.

At the end of the fold return motion, the capillary is contacting thetop of the bump 56 and pinching the wire between the tip of thecapillary 11 and the bump, as shown in FIG. 5I. At this point, the wirehas been pinched, but not severed. Also, at this point, the second ofthe five aforementioned portions of the overall folded forward wire loop(i.e., the fold 57) is completed. As the wire has not been severed sincethe beginning of the process, the fold 57 is continuous with the bump56.

The wire is then bonded to the top of the bump 56. Heat and/orultrasonic energy may be applied to facilitate bonding of the compressedportion of the wire to the top of the bump 56. However, the bondingprocess need comprise nothing more than simply pinching the wire betweenthe tip of the capillary and the ball without severing the wire. One maycall this bond a stitch bond or a stitch-like bond, but the wire shouldnot be severed. At this point, the third of the five aforementionedportions of the overall loop (i.e., bond 58) is completed. FIG. 53 showsthe process at this point, which is essentially the same position asshown in FIG. 51 since the capillary typically does not move duringbonding.

The capillary is now moved toward the second bond site through a set ofcoordinated xyz motions to form the desired wire loop shape (the fourthportion of the overall loop) and to position the capillary above thesecond bond site 65. FIGS. 5K and 5L show the position of the capillary11 at two points along an exemplary trajectory to the second bond site65.

The coordinated xyz motion can be relatively simple, comprising astraight xy motion toward the second bond site. However, typically thereis motion in the z direction to help form the wire loop into the mostpreferable shape. As the wire has still not been severed since thebeginning of the process, the wire loop 59 is continuous with the bump56, fold 57, and bond 58 at the first bond site.

Next, the capillary is lowered to pinch the wire between the second bondsurface 65 and the tip of the capillary 11 and the wire is stitch bondedto the second bond site. Heat and/or ultrasonic energy may be applied tofacilitate bonding. At this point, the wire has been pinched, but hasnot been fully severed, as shown in FIG. 5M. The capillary 11 is thenraised with the clamps 18 still open and with the wire still attached tothe stitch bond 60 such that a wire tail 69 pays out of the capillary11. FIG. 5N illustrates the position of the capillary at this point inthe process. The clamps 18 are then closed and the capillary 11 israised further to snap the wire at the stitch bond 60 as shown in FIG.5O. The fifth portion of the overall folded forward wire loop, i.e., thestitch bond 60, is now completed and the entire folded forward loopingprocess is concluded.

The main purposes of the bump 56 are to prevent direct contact of thecapillary with the bond pad and to raise the height (z direction) fromwhich the wire exits the first bond site. Specifically, the wire exitsthe first bond site at so low of an angle that, if not for the extraheight above the die surface provided by starting the wire loop on topof a bump, the wire loop 59 might otherwise contact the die surfaceintermediate the first and second bond sites.

The primary purpose of forming the fold 57 on top of the bump is so thatthe wire exits the first bond site generally horizontally and pointingtoward the second bond site, thus creating a low loop height. The foldis generally elliptical in shape with its major axis in the xy plane andthe wire exits the end of the fold generally horizontally and generallypointing directly toward the second bond site. This orientation is to becontrasted with the generally straight upward orientation of the wire asit exits the first bond site in a conventional forward wire loop.Accordingly, the looping technique of the present invention providesultra-low loop heights because the wire exits the ball bond sitepointing horizontally rather than vertically upward.

In addition, the impact to the die is reduced relative to conventionalreverse ball bonding because it does not perform a normal second bond ontop of the bump, as is the case with reverse looping. The wire is onlyslightly compressed to form the loop and bond on top of the ball as inFIG. 7A in comparison to a normal stitch bond similar to FIG. 7B as inreverse bonding.

Further, finer pitches can be achieved with the present inventionrelative to reverse ball bonding because the bump is not compressed andsquished out laterally as much as in the reverse wire looping technique.

The wire bonding machine is controlled by motion control systemcomprising control circuitry that can cause the machine to perform theprocesses described herein. Commonly, the circuitry comprises a digitalprocessing device such as a programmed general purpose computer, adigital signal processor, a state machine, a combinational logiccircuit, a microprocessor, an application specific integrated circuit,or any other known digital processing means. If the circuitry comprisesa computer, the invention may reside largely, if not exclusively, in thesoftware for programming the computer to control the wire bondingmachine to perform the processes described herein.

By optimizing the various motion components described in connection withFIG. 4, we can achieve desired shape with low loop height and no neckdamage. As an example, FIG. 6 shows exemplary parameters that were usedto form the fold shown in FIG. 7A and subsequently the loop profileshown in FIGS. 8A and 8B. The first three motions (separation height 75,fold offset 76 and fold factor 77) collectively determine the amount ofthe wire in the fold and the shape of the fold. If these motions are toolarge, a larger fold than desired may be formed. If these motions aretoo small, a fold may not be formed at all and the neck region of thewire could be damaged.

We have found through experimentation that a separation height and afold offset slightly larger than the wire diameter (e.g., about 1.01 to1.55 times the wire diameter) achieves excellent results. Furthermore,the fold factor should be a positive value. In the example of FIG. 7A,the separation height 75 is 1.5 mil, the fold offset 76 is 1.3 mil andthe fold factor 77 is 1 mil for a wire of a diameter of 1 mil). Thesesettings pay out the proper amount of wire and angle the wire around 30degrees from the vertical before the fold return motion 78 starts.

The fold return motion 78 determines the final shape of the bump. In theparticular machine we used, the fold return motion 78 is specified bytwo parameters. Specifically, (1) the aforementioned fold return offsetparameter (which, along with the fold offset, dictates the horizontalcomponent of the fold return motion) and (2) the bump height (which,along with the fold factor, dictates the vertical component of thereturn motion).

To form a good fold with enough deformation to sustain the fold withoutoverly flattening the bump, bump height normally should be a negativevalue (bump height being a vertical distance from the separationheight). In this example, the bump height is −1.25 mil and theseparation height is 1.5 mil. Thus, the final position of the capillaryis about 0.25 mil above the bump 56. This provides just enoughflattening of the wire to form the fold without flattening the bumpsignificantly. The fold return offset in this example is 0.5 ml, whichmeans that the final position of the capillary after the fold returnmotion 78 is offset 0.5 mil horizontally from the center of the bump(away from the second bond 60). These settings ensure that the site ofthe bond 58 is centered on top of the bump 56.

The wire loop resulting from bonding using these parameters is shown inFIG. 8. Over multiple experimental samples, the average loop heightusing these parameters was 2.3 mil. The maximum loop height was 2.5 mil.

Having thus described a few particular embodiments of the invention,various alterations, modifications, and improvements will readily occurto those skilled in the art. Such alterations, modifications andimprovements as are made obvious by this disclosure are intended to bepart of this description though not expressly stated herein, and areintended to be within the spirit and scope of the invention.Accordingly, the foregoing description is by way of example only, andnot limiting. The invention is limited only as defined in the followingclaims and equivalents thereto.

1. A wire loop interconnect between a first bond site and a second bondsite comprising: (1) a ball bond at the first bond site; (2) a fold ofwire continuous with the ball bond, at least a portion of the fold ofwire being bonded on top of the ball bond, the fold of wire being formedusing the steps of, in order: (2.1) raising a capillary above the ballbond formed at the first bond site a distance between 1.01 and 1.55times the diameter of the wire, (2.2) then moving the capillaryhorizontally away from a second bond site a distance between 1.01 and1.55 times the diameter of the wire, and (2.3) then moving the capillaryback toward the ball bond at the first bond site; (3) a wire loopbetween the fold of wire and the second bond site, the wire loopcomprising wire continuous with the fold of wire; and (4) a bond at thesecond bond site terminating the wire loop interconnect, whereby thewire loop has a loop height less than or equal to 2.5 mils.
 2. The wireloop interconnect of claim 1 wherein the fold of wire is generallyelliptical in shape.
 3. The wire loop interconnect of claim 1 whereinthe wire loop exits the top of the ball bond toward the second bond sitesubstantially horizontally.
 4. The wire loop interconnect of claim 1wherein the first bond site is higher than the second bond site.
 5. Thewire loop interconnect of claim 4 wherein the first bond site is on asemiconductor die and the second bond site is on a substrate carryingthe semiconductor die.
 6. A wire bonding machine comprising: acapillary; a wire delivery system for supplying wire through a bore inthe capillary; and a motion control system for controlling motion of thecapillary, the motion control system including circuitry for: (1)forming a ball bond at a first bond site; (2) forming a fold of wirecontinuous with the ball bond, step (2) including in order: (2.1)raising the capillary above the ball bond formed on the first bond sitea distance between 1.01 and 1.55 times the diameter of the wire, (2.2)then moving the capillary horizontally away from a second bond site adistance between 1.01 and 1.55 times the diameter of the wire, and (2.3)then moving the capillary back toward the ball bond on the first bondsite; (3) bonding the fold of wire on top of the ball bond; (4)continuously forming a wire loop between the wire fold and the secondbond site; and (5) forming a bond at the second bond site to terminatethe wire loop, whereby the wire loop has a loop height less than orequal to 2.5 mils.
 7. The wire bonding machine of claim 6 wherein thecircuitry for performing task (3) causes the wire loop to exit the topof the ball bond substantially horizontally.
 8. The wire bonding machineof claim 6 wherein the circuitry for performing task (2.3) comprisescircuitry for moving the capillary horizontally a distance less than thehorizontal distance traversed in step (2.2).
 9. The wire bonding machineof claim 6 wherein the circuitry comprises a digital processing device.10. The wire bonding machine of claim 9 wherein the digital processingdevice comprises a computer running computer software.
 11. A computerreadable product for controlling a wire bonding machine comprising acapillary, the computer readable product comprising computer executableinstructions for: (1) bonding a wire to a first bond site to form a bumpon the first bond site; (2) forming a fold of wire continuous with thebump, step (2) including in order: (2.1) raising the capillary above thebump formed on the first bond site a distance between 1.01 and 1.55times the diameter of the wire, (2.2) then moving the capillaryhorizontally away from a second bond site a distance between 1.01 and1.55 times the diameter of the wire, and (2.3) then moving the capillaryback toward the bump on the first bond site; (3) bonding the wire on topof the bump after forming the fold of wire; (4) continuously forming awire loop between the top of the bump and the second bond site; and (5)forming a bond at the second bond site to terminate the wire loop,whereby the wire loop has a loop height less than or equal to 2.5 mils.12. The computer readable product of claim 11 wherein the computerexecutable instructions for forming the fold of wire causes the fold ofwire to be generally elliptical in shape.
 13. The computer readableproduct of claim 11 wherein the computer executable instructions forbonding the wire on top of the bump causes the wire to exit from the topof the ball bond substantially horizontally.